Nearly 1,000 patients of PeaceHealth Southwest Medical Center are being told to get tested for hepatitis C out of concern that they may have been exposed to the virus by a former hospital employee.

PeaceHealth sent out letters on Monday to 936 patients who had contact with the former employee, whose name and position were not disclosed. The person is now under investigation by PeaceHealth and Clark County Public Health on suspicion of taking drugs for patient use and diverting them for personal use. The employee worked for PeaceHealth from mid 2012 to 2014.

Health officials said they believe the risk of infection is low and that they don't have any evidence that the former employee exposed anyone. But they said they want to be cautious.

Hepatitis C is typically spread by direct blood-to-blood contact, said Theresa Cross, with Clark County Public Health. It can be spread by using a needle twice, for instance, she said.

Chronic hepatitis C is the leading cause of cirrhosis and liver cancer and the most common reason for liver transplantation in the United States, according to PeaceHealth. About 15,000 people die every year from hepatitis C related liver disease.

Officials said Tuesday that one patient who was at the hospital in August 2012 was found four months later to have hepatitis C. The patient had no apparent risk factors for hepatitis C except for the patient's stay at PeaceHealth at which drugs were delivered intravenously. The patient had been in the care of the former employee, the hospital said.

Although no transmission source has been identified, health officials stressed that they do not have any evidence that the patient's infection originated with the former employee. The employee did not come under investigation for possible drug diversion until February. Hospital officials would not disclose whether the employee has hepatitis C due to privacy concerns.